A device to measure and to control flow and quantity of heat is known from DE-OS 33 12 140. To measure quantity of heat, the difference of the initial and return temperature of a heat circuit as well as the opening in time of an OPEN/CLOSED valve as well as the calibration value for the flow are multiplied with each other. Instead of the calibration value of the flow it is also possible to find the pressure difference through the valve. The valve is controlled by means of a volume temperature sensor,
A quantity-regulating valve where the pressure and the temperature are measured before and after the valve and the opening cross-section of the valve is measured and further processed by a computer is known from DE-OS 37 00 898.
Furthermore a quantity regulating valve where means for the measurement of the differential pressure through the valve are installed within a housing is known from EP-OS 0 309 643.
Even if the actual pressure difference is measured there remains the problem that intolerable measuring errors occur when flow and/or temperature differences are very small. The occurring problems are pointed out in the DE-Z (German periodical) "Fernwarme international" 17(1988), vol. 1, pages 23-35. It is known that extremely small flow and/or temperature differences which are beyond the measuring range of the measuring means occur especially during transitional periods.
The instant invention has as its object to create a device to measure and to control flow and/or heat quantities of a flow medium in a conduit at low manufacturing cost capable of sufficiently and precisely measuring and controlling flow and/or heat quantities even when the flow and/or temperature differences are very small.